Sorry to hear your troubles... I finished this same job a few weeks back. Replacing the original lines (lower one seeping at the cooler) Indeed, what an oily PITA it was.

I also installed a new trucktec line and agree it is not as quality a part as the original. The rubber is "flimsier" and I bet is only single layer. Shame since the package indicates its made in Germany.

I cut out the originals and they are indeed double layered (hose within a hose).

I've only driven a 100 miles or so since the replacement. So far no leakage. Dealing with pilot bearing issue, trans is out of the car again.

I actually found a newer upper used OEM replacement hose in the trunk of a w123 at the boneyard.

I also nabbed an oil cooler from a w126, learning from the board here to have a spare.

Surprisingly, the oil cooler fittings and upper cooler fitting broke free without much effort. But the lower cooler fitting was seized... PB blaster or heat, no joy. The original cooler is now still sitting on my garage floor.

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'82 300TD
'84 300D OM617
Auto to 4spd Manual Swap 716.210
'85 300SD 2.88 Diff (Direct Swap)
W140 HD Rear Springs w/ bilstein shocks (SLS Delete)
'83 300SD Big Brake Booster Swap
Late model 240D Manual HVAC Swap
W124 Outside Temp Gauge
Aftermarket Keyless Entry

'84 300D RIP